Apparatus for detecting alternating current zero cross and voltage

ABSTRACT

A detection apparatus has an alternating-current voltage input unit and a generation circuit. The generation circuit generates a superimposition signal in which information indicating a timing of a zero cross in an alternating-current voltage inputted into the input unit and information indicating a voltage level of the alternating-current voltage are superimposed.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an apparatus for detecting alternatingcurrent zero cross and voltage.

Description of the Related Art

Typically, an image forming apparatus uses a commercial alternatingcurrent power supply as a power supply source. There are cases in whichan image forming apparatus controls power supplied to a load using analternating current zero cross as a reference. A detection circuit fordetecting such a zero cross is proposed in Japanese Patent Laid-Open No.2006-216657.

However, there are countries in which there is much variation inalternating-current voltage supplied from a commercial alternatingcurrent power supply. In order to protect a power supply apparatus and aload from such variation, a load may be controlled appropriately inaccordance with the alternating-current voltage detected by thedetection circuit. An alternating-current voltage detection circuit isproposed by Japanese Patent Laid-Open No. 2003-098860.

A control apparatus such as a microcomputer may control an image formingapparatus by obtaining a zero cross signal that a zero cross detectioncircuit outputs and a voltage signal that an alternating-current voltagedetection circuit outputs. However, since the two detection circuits areindependent, the control apparatus requires many circuit components suchas two signal lines and two input ports.

SUMMARY OF THE INVENTION

The present invention reduces the number of signal lines fortransferring a zero cross and an alternating-current voltage.

The present invention provides a detection apparatus comprising: analternating-current voltage input unit; and a generation circuitconfigured to generate a superimposition signal in which informationindicating a timing of a zero cross in an alternating-current voltageinputted into the input unit and information indicating a voltage levelof the alternating-current voltage are superimposed.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a detection apparatus in a firstembodiment.

FIG. 2A is a view for describing a pulse signal generation principle.

FIG. 2B is a view for describing a relationship between an inputalternating-current voltage and a pulse signal.

FIG. 2C is a view for describing a relationship between an inputalternating-current voltage and a pulse width.

FIG. 3 is a view for describing a function of a microcomputer.

FIG. 4 is a view that illustrates a voltage table.

FIG. 5 is a view illustrating a detection apparatus in a secondembodiment.

FIG. 6A is a view for describing a pulse signal generation principle.

FIG. 6B is a view for describing a relationship between an inputalternating-current voltage and a pulse width.

FIG. 6C is a view for describing a relationship between an inputalternating-current voltage and a pulse width.

FIG. 7 is a view illustrating a detection apparatus in a thirdembodiment.

FIG. 8A is a view for describing a pulse signal generation principle.

FIG. 8B is a view for describing a relationship between an inputalternating-current voltage and a pulse width.

FIG. 9 is a view illustrating a detection apparatus in a fourthembodiment.

FIG. 10A is a view for describing a pulse signal generation principle.

FIG. 10B is a view for describing a relationship between an inputalternating-current voltage and a pulse width.

FIG. 11 is a view illustrating a detection apparatus in a fifthembodiment.

FIG. 12A is a view for describing a pulse signal generation principle.

FIG. 12B is a view for describing a relationship between an inputalternating-current voltage and a pulse width.

FIG. 13 is a view illustrating a detection apparatus in a sixthembodiment.

FIG. 14A is a view for describing a pulse signal generation principle.

FIG. 14B is a view for describing a relationship between an inputalternating-current voltage and a pulse width.

FIG. 15 is a view for illustrating an image forming apparatus.

DESCRIPTION OF THE EMBODIMENTS

In accordance with the present invention, a detection apparatus thatgenerates a superimposition signal in which information indicating atiming of a zero cross in an alternating-current voltage and informationindicating a voltage level of the alternating-current voltage aresuperimposed is provided. The number of signal lines is reduced thereby.More specifically, a detection apparatus that generates a pulse signalincluding a first edge that indicates a timing of a zero cross in analternating-current voltage and a second edge for which a time intervalin relation to the first edge changes in accordance with the voltagelevel of the alternating-current voltage is provided.

First Embodiment

In a first embodiment, a first edge that indicates the timing of thezero cross is generated by the forward voltage being applied to a diodedropping to less than or equal to a threshold. When a voltage that iscorrelated with an alternating-current voltage applied to a gate of aFET connected in series with a diode exceeds the threshold, the FETconducts electricity, thereby causing the diode to conduct electricity,and a second edge indicating the voltage level of thealternating-current voltage is generated. This uses the property thatthe timing at which the voltage level exceeds the threshold will beearlier if the voltage level of the alternating-current voltage ishigher, and at which the timing of the voltage level exceeds thethreshold will be later if the voltage level is lower. FET is anabbreviation for field-effect transistor. A microcomputer recognizes atemporal position of the first edge as a zero cross point of thealternating-current voltage. Also, the microcomputer recognizes the timeinterval from the second edge until the first edge as the voltage levelof the alternating-current voltage.

FIG. 1 is a circuit diagram of a detection apparatus 100 for detecting avoltage level and zero cross of an alternating-current voltage in thefirst embodiment. A zero cross detection unit 101 a is a circuit fordetecting a timing of a zero cross of the alternating-current voltagesupplied from the commercial alternating current power supply AC. Notethat the alternating-current voltage supplied from the commercialalternating current power supply AC is inputted into an input unit 110such as an input terminal. A voltage detection unit 106 a is a circuitfor detecting a voltage level (effective value) of thealternating-current voltage supplied from the commercial alternatingcurrent power supply AC.

A photocoupler PC has a light emitting diode D1 and a phototransistorQ1, and is an insulation element for insulating a primary side and asecondary side of the photocoupler PC. In FIG. 1, the commercialalternating current power supply AC is connected to a primary side. Amicrocomputer 105 is connected to a secondary side. The light emittingdiode D1 is turned on or turned off in accordance with information onthe primary side. The phototransistor Q1 receives light from the lightemitting diode D1, and outputs a signal according to the received light.A diode D2 is formed in parallel with the light emitting diode D1. Thediode D2 conducts electricity in a case where the alternating-currentvoltage supplied from the commercial alternating current power supply ACis a negative voltage and does not conduct electricity in a case whereit is positive. The end-to-end voltage of the light emitting diode D1 ofthe photocoupler PC is thereby suppressed to a tolerable voltage of thelight emitting diode D1 or less. A resistor R1 is a current-limitingresistor that protects the light emitting diode D1 by restricting thecurrent that would flow to the light emitting diode D1.

The voltage detection unit 106 a is connected in series to the lightemitting diode D1. The voltage detection unit 106 a has a leveldetection unit 107 for detecting the voltage level of thealternating-current voltage supplied from the commercial alternatingcurrent power supply AC and a FET Q2 for conducting electricity or notconducting electricity in accordance with the voltage level. The leveldetection unit 107 has a resistor R3 and a capacitor C1 which configurea low-pass filter (LPF), and imparts a phase delay to a voltagecorrelated to the alternating-current voltage and applies the voltage tothe FET Q2. When the gate voltage of the FET Q2 exceeds the gatethreshold of the FET Q2, electricity is conducted between the drain andthe source of the FET Q2. When the FET Q2 conducts electricity at thetime that the voltage applied to the light emitting diode D1 exceeds theforward voltage VF, a forward current flows to the light emitting diodeD1. A collector of the phototransistor Q1 is pulled up to the powersource voltage Vcc (example: 3.3V) by a resistor R2. Accordingly, thephototransistor Q1 generates a pulse signal having a binary voltagelevel of H (approximately 3.3V) or L (approximately 0V), and inputs thepulse signal into an input port 104 of the microcomputer 105. H is anabbreviation for high level. L is an abbreviation for low level. Notethat when the light emitting diode D1 turns on, the phototransistor Q1conducts electricity, and the pulse signal is L. When the light emittingdiode D1 is turned off, the phototransistor Q1 does not conductelectricity, and the pulse signal is H.

FIG. 2A illustrates a voltage waveform W1 of the commercial alternatingcurrent power supply AC, a voltage waveform W2 of the gate terminal ofthe FET Q2, and a voltage waveform W3 of the pulse signal. The abscissaindicates time. The ordinate indicates voltage. The voltage of thecommercial alternating current power supply AC is assumed to be 100Vrms. The voltages of the other waveforms are voltages in the range ofseveral V. Here, in order to represent all waveforms within the samegraph, for convenience, the voltage of the commercial alternatingcurrent power supply AC is shown graphically at 1/20 of its actualmagnitude. An operation state W4 of the light emitting diode D1 of thephotocoupler PC and an operation state W5 of the FET Q2 are illustratedby overlapping these voltage waveforms. The reverse direction indicatesthat voltage in the reverse direction is being applied to the lightemitting diode D1. Forward direction indicates that voltage in theforward direction is being applied to the light emitting diode D1. ONindicates a conductive state. OFF indicates a non-conductive state.

The light emitting diode D1 enters a conductive state when the voltageof the commercial alternating current power supply AC exceeds apredetermined value (approximately 1.0V which is the forward voltage VFof the light emitting diode of the photocoupler PC). In this way, theforward voltage VF is much smaller as compared to the 100 Vrms which isthe effective value of the alternating-current voltage of the commercialalternating current power supply AC. Accordingly, the timing of theswitch between when the light emitting diode D1 conducts electricity towhen it does not conduct electricity substantially indicates the zerocross timing of the commercial alternating current power supply AC.

In the first embodiment, the light emitting diode D1 is connected inseries with the FET Q2. Accordingly, the zero cross timing can only bedetected when the FET Q2 is conducting electricity. As illustrated inFIG. 2A, in the state in which the FET Q2 is conducting electricity, andwhen the zero cross timing of the commercial alternating current powersupply AC arrives, the light emitting diode D1 switches from aconductive state to a non-conductive state. A rising edge (the timing atwhich the level of the pulse signal changes from L to H) of the pulsesignal is generated thereby.

Meanwhile, the voltage of the commercial alternating current powersupply AC is inputted into the LPF formed by the resistor R3 and thecapacitor C1. The cut-off frequency of the LPF is set so that the phaseof voltage is delayed by between several tens of degrees to 90 degreesin the range of 50 Hz to 60 Hz which is the frequency of the commercialalternating current power supply AC. By this operation of the LPF, thewaveform of the gate voltage of the FET Q2 becomes the voltage waveformW2 as illustrated by the broken line in FIG. 2A. The gate threshold ofthe FET Q2 may be 3V, for example. In such a case, the FET Q2transitions into a conductive state at the point in time when the gatevoltage exceeds 3V. By the influence of the phase delay due to the LPF,the timing at which the FET Q2 is conducting electricity and the timingat which it is not conducting electricity are delayed in relation to thephotocoupler PC. The photocoupler PC and the FET Q2 are connected inseries to the commercial alternating current power supply AC.Accordingly, only in a case where both the photocoupler PC and the FETQ2 are conducting electricity is the information transferred to thesecondary side. The falling edge of the pulse signal, which is thetiming of the onset of information transfer to the secondary side, isgenerated by the FET Q2 conducting electricity. The rising edge, whichis the timing at which information transfer to the secondary side ends,is generated by the light emitting diode D1 switching from conductingelectricity to not conducting electricity.

FIG. 2B illustrates voltage waveforms W1 through W3 where the voltage ofthe commercial alternating current power supply AC is changed in four20V increments in the range from 80V to 140V. The temporal position ofthe rising edge generated by the light emitting diode D1 ceasing toconduct electricity does not change much even though the voltage of thecommercial alternating current power supply AC is changed. The forwardvoltage VF of the light emitting diode D1 is sufficiently small inrelation to the voltage of the commercial alternating current powersupply AC. Accordingly, the position of the rising edge is not affectedmuch by the difference in gradient (dv/dt) due to the change in thevoltage of the commercial alternating current power supply AC.

Meanwhile, the falling edge generated when the FET Q2 conductselectricity changes greatly in accordance with the change in voltage ofthe commercial alternating current power supply AC. This is because thegate threshold of the FET Q2 (3V) and the gate voltage of the FET Q2(approximately between 4 Vpeak and 5 Vpeak) are close to each other.Accordingly, the position of the falling edge is influenced by thedifference in gradient (dv/dt) of the gate voltage of the FET Q2 due tothe change in voltage of the commercial alternating current power supplyAC. As FIG. 2B illustrates, the time over which the gate voltage of theFET Q2 exceeds the gate threshold of the FET Q2 differs greatlydepending on the voltage of the commercial alternating current powersupply AC. Accordingly, the falling edge generation timing changesgreatly depending on the voltage of the commercial alternating currentpower supply AC. The timing at which the FET Q2 ceases to conductelectricity also changes greatly depending on the voltage of thecommercial alternating current power supply AC similarly to the case ofconducting electricity. However, the LPF is designed so that at thetiming at which the FET Q2 ceases to conduct electricity, the lightemitting diode D1 is invariably not conducting electricity. Thereby, thepulse signal does not depend on the timing at which the FET Q2 ceases toconduct electricity.

FIG. 2C illustrates a relationship between the pulse width and thevoltage of the pulse signal. The pulse width means the time from whenthe falling edge is detected to when the rising edge is detected. Theabscissa indicates the effective value of the alternating-currentvoltage supplied from the commercial alternating current power supplyAC. The ordinate indicates the pulse width of the pulse signal. PW2indicates the pulse width in a typical case where there is no variationin the circuit component. PW1 indicates properties in a case where thepulse width reaches a maximum due to variation in the circuit component.PW3 indicates properties in a case where the pulse width reaches aminimum due to variation in the circuit component. The variation of theresistor R3 is ±1%. The variation of the capacitor C1 is ±10%. Thevariation of the gate threshold of the FET Q2 is ±3%. In the firstembodiment, the variation of the capacitor C1 brings about a largeeffect on the pulse width. Accordingly, by employing a variable resistoras the resistor R3 and setting the resistance value appropriately inrelation to the variation of the capacitor C1, the voltage of thecommercial alternating current power supply AC will be detected at aneven higher precision.

FIG. 3 illustrates functions of the microcomputer 105. The microcomputer105 may be realized by a CPU, may be realized by an ASIC, an FPGA, orthe like, and may be realized by a combination thereof. ASIC is anabbreviation for application specific integrated circuit. FPGA is anabbreviation for field-programmable gate array. A control program may bestored in a storage apparatus 310. Here, it is assumed that thefollowing function are realized by a CPU executing a control program.

A load control unit 301 is able to recognize a zero cross timing of thealternating-current voltage of the commercial alternating current powersupply AC by detecting the rising edge of the pulse signal inputted intothe input port 104. A first counter 302 measures the time betweenadjacent rising edges in the pulse signal. This time corresponds to oneperiod. The reciprocal of one period is the frequency. Note that thetime between adjacent falling edges may also be measured. A frequencydetermination unit 303 converts the count value of the first counter 302into a frequency by referencing a frequency table 311 stored in thestorage apparatus 310. Note that a function may be used in place of thefrequency table 311. A second counter 304 measures the time (pulsewidth) from the falling edge until the rising edge of the pulse signal.A voltage determination unit 305 converts the count value of the secondcounter 304 into a voltage value by referencing a voltage table 312stored in the storage apparatus 310. Note that a function (approximationexpression) may be used in place of the voltage table 312.

FIG. 4 illustrates the voltage table 312 for converting the pulse widthmeasured by the second counter 304 into a voltage value. Here, 50 Hz isenvisioned as the frequency of the alternating-current voltage, butthere are regions in which a 60 Hz frequency is used. Accordingly, thestorage apparatus 310 may have voltage tables 312 for each frequency. Insuch a case, the voltage determination unit 305 may select the voltagetable 312 based on the frequency which is determined by the frequencydetermination unit 303. Alternatively, the storage apparatus 310 maystore a single normalized voltage table 312 and a correction coefficientfor each frequency. The voltage determination unit 305 may select thecorrection coefficient based on the frequency determined by thefrequency determination unit 303 and correct the voltage value obtainedfrom a count value and the voltage table 312 by the correctioncoefficient. The voltage table 312 illustrated in FIG. 4 is a table forobtaining voltage values in increments of 5V. However, a higherresolution conversion table may be employed in a case where detection ofcommercial alternating current power supply AC voltages at a higherresolution is desired. Alternatively, even higher resolution voltagevalues may be calculated by using a function such as an approximationexpression.

In FIG. 3, the load control unit 301, triggered by the voltage valuedetermined by the voltage determination unit 305 and the zero crosstiming, controls a load 320. For example, if the load 320 is a fixingdevice of an image forming apparatus of an electrophotographic type, theload control unit 301 can control the power inputted into the heater ofthe fixing device by wave number control. Wave number control meansadjusting the power applied to a heater in units of waves (a half periodof the alternating current). The load control unit 301 can recognize thestart position of a half period based on the zero cross timing.Furthermore, since the load control unit 301 can also obtain the voltagelevel of the alternating-current voltage, it can determine the power tobe inputted into the heater from the voltage level, and supply to theload 320 the alternating current of the required wave number using thezero cross timing as a reference. Note that the image forming apparatusis only one example, and the first embodiment can be applied to anyelectric device comprising a load that operates upon supply of analternating current.

In this way, in accordance with the first embodiment, an informationsignal in which information indicating the timing of a zero cross andinformation indicating a voltage level of an alternating-current voltageare superimposed is generated and transmitted. Accordingly, the numberof signal lines and input ports 104 for transferring the informationsignal can be reduced. In other words, it is possible to detect the zerocross and the alternating-current voltage with a reduced number ofcircuit components.

In particular, in the first embodiment, the zero cross timing isrepresented by the temporal position of the rising edge of the pulsesignal. Also, the alternating-current voltage of the commercialalternating current power supply AC is represented by the time intervalbetween the rising edge and the falling edge of the pulse signal.Accordingly, the microcomputer 105 is enabled to recognize the zerocross timing and the alternating-current voltage from a pulse signalwhich is inputted from a single input port 104. Note that the timeinterval between rising edges and the time interval between fallingedges are both fixed. Accordingly, the microcomputer 105 can obtain thefrequency of the alternating-current voltage from either time interval.

In the first embodiment, the voltage waveform of the commercialalternating current power supply AC is envisioned to be a sinusoidalwave. The conversion table stored in the storage apparatus 310 isgenerated assuming a sinusoidal wave. There may be cases in which avoltage in something other than a sinusoidal wave, such as a rectangularwave, is supplied from the commercial alternating current power supplyAC. In such a case, it is possible for the microcomputer 105 to detectthat a rectangular wave or the like was inputted. The gradient (dv/dt)of the voltage of a rectangular wave is much greater as compared to thegradient of the voltage of a sinusoidal wave. Accordingly, the pulsewidth of a rectangular wave is much longer than the pulse width of asinusoidal wave. Accordingly, the microcomputer 105 may decide that thewaveform of the alternating-current voltage is not a sinusoidal wavewhen the pulse width measured by the second counter 304 exceeds apredetermined threshold. The voltage determination unit 305 may be incharge of this decision. When the load control unit 301 receives adetermination signal meaning that the waveform of thealternating-current voltage is not a sinusoidal wave from the voltagedetermination unit 305, the load control unit 301 causes the supply ofalternating current to the load 320 to stop. For example, the loadcontrol unit 301 stops the supply of alternating current by switchingoff a switch element such as a TRIAC or the like. With this, it becomespossible to protect the load 320.

Note that it is not necessary that the waveform of thealternating-current voltage be a sinusoidal wave in the firstembodiment. If the gradient (dv/dt) of the alternating-current voltagechanges in accordance with the effective value, the first embodiment canbe applied.

In FIG. 1, the LPF is formed by using the resistor R3 and the capacitorC1. Also, the FET Q2 is employed as a switch element. However, anycircuit that can appropriately adjust the phase of thealternating-current voltage may be used. In place of the FET Q2, asemiconductor switch such as a transistor, a relay, or the like can beemployed if the switch element can switch between a conductive state anda non-conductive state in accordance with the voltage level of thecontrol signal.

A photocoupler PC in which a primary side and a secondary side areinsulated is employed in FIG. 1, but this is not required. In place ofthe photocoupler PC, a switch element such as a semiconductor switch ora relay may be employed. Alternatively, configuration may be taken suchthat the photocoupler PC is removed, and the drain terminal of the FETQ2 is connected to the input port 104 directly.

Second Embodiment

The second embodiment improves the detection apparatus 100 of the firstembodiment to improve the voltage level detection precision.Specifically, by increasing the change in the pulse width in accordancewith the difference of the voltage level, the dynamic range of thevoltage level widens. In other words, the amount of change in theposition of the second edge in relation to the amount of change of thevoltage level of the alternating-current voltage becomes greater.

FIG. 5 illustrates the detection apparatus 100 of the second embodiment.In the second embodiment, the same reference numerals are given tocircuit elements that are the same as in the first embodiment, anddescription of the first embodiment is invoked. In the secondembodiment, the voltage detection unit 106 a is replaced with a voltagedetection unit 106 b. The voltage detection unit 106 b has a leveldetection unit 501, a timing adjusting unit 502, and a voltagegeneration unit 503. The alternating-current voltage supplied from thecommercial alternating current power supply AC is inputted into thelevel detection unit 501. The level detection unit 501 is avoltage-dividing circuit formed by a resistor R4 and a resistor R5, andthe alternating-current voltage supplied from the commercial alternatingcurrent power supply AC is converted into an alternating-current voltageproportional thereto, which is then outputted.

The alternating-current voltage of the commercial alternating currentpower supply AC is inputted into the timing adjusting unit 502. Thetiming adjusting unit 502 is a circuit for adjusting the timing at whichthe FET Q3 switches from on (conducting electricity) to off (notconducting electricity). The timing adjusting unit 502 is an LPFconfigured by a resistor R6 and a capacitor C2. In other words, thetiming adjusting unit 502 delays the phase of the alternating-currentvoltage and outputs the alternating-current voltage. A diode D3 isarranged with the objective of separating the level detection unit 501and the timing adjusting unit 502. The current outputted from the leveldetection unit 501 and the current outputted from the timing adjustingunit 502 both flow into a resistor R7. In other words, the resistor R7functions as an adder that adds these currents and converts the sum ofthe currents into a voltage. In this way, the resistor R7 adds thevoltage detected by the level detection unit 501 and the voltageoutputted from the timing adjusting unit 502.

The voltage generation unit 503 is a circuit for generating adirect-current voltage from the alternating-current voltage suppliedfrom the commercial alternating current power supply AC. A resistor R8and a resistor R9 of the voltage generation unit 503 form avoltage-dividing circuit which divides the alternating-current voltageand outputs an output voltage (the divided alternating-current voltage).A diode D4 is a rectification element for performing a half waverectification of the alternating-current voltage generated by thevoltage-dividing circuit. A capacitor C3 is a smoothing element forgenerating a direct current by smoothing the pulsating flow that thediode D4 outputs. The voltage generated by the voltage generation unit503 is divided by a voltage-dividing circuit which is formed by aresistor R10 and a resistor R11, and the output voltage is applied tothe gate of the FET Q3. Similarly, the end-to-end voltage of theresistor R7 is applied to the gate of the FET Q3 via the capacitor C4.In other words, the end-to-end voltage of the resistor R7 and thedirect-current voltage from the voltage generation unit 503 aresuperimposed and the resulting voltage is applied to the gate of the FETQ3. Note that the capacitor C4 has a role of cutting the direct currentcomponent in the end-to-end voltage of the resistor R7. In a case wherethis direct current component does not affect the operation of the FETQ3 much, the capacitor C4 may be omitted. The reason that thedirect-current voltage from the voltage generation unit 503 is dividedby the resistor R10 and the resistor R11 and the output voltage isapplied to the gate of the FET Q3 is that this reduces the effect of thediode D4 and the capacitor C3 of the voltage generation unit 503.Thereby, the voltage detection precision improves.

FIG. 6A illustrates the waveform W1 of the alternating-current voltage,the waveform W2 of the voltage applied to the gate of the FET Q3, andthe waveform W3 of the pulse signal in the second embodiment. Thealternating-current voltage from the division in the level detectionunit 501 and the output voltage of the timing adjusting unit 502 areadded by the resistor R7. As the waveform W2 illustrates, the waveformof the voltage applied to the gate is a waveform resulting fromincreasing the amplitude of part of a sinusoidal wave. By adding theoutput voltage of the timing adjusting unit 502 to the output voltage ofthe level detection unit 501, the timing at which the FET Q3 ceases toconduct electricity is adjusted to be after the timing at which thelight emitting diode D1 ceases to conduct electricity. Because the lightemitting diode D1 and the FET Q3 are connected in series, the risingedge of the pulse signal is generated by the light emitting diode D1ceasing to conduct electricity, and the falling edge is generated by theFET Q3 conducting electricity.

FIG. 6B illustrates voltage waveforms W1 through W3 where the voltage ofthe commercial alternating current power supply AC is caused to changein four 20V increments in the range from 80V to 140V. The timing atwhich the rising edge generated by the light emitting diode D1 ceases toconduct electricity does not change much even though the voltage levelof the commercial alternating current power supply AC changes.Meanwhile, the timing at which the gate voltage of the FET Q3 exceedsthe gate threshold of the FET Q3 changes greatly depending on thevoltage level of the commercial alternating current power supply AC. Inother words, the timing of the falling edge changes greatly depending onthe voltage level of the commercial alternating current power supply AC.Also, since the pulse width changes greatly depending on the voltagelevel of the commercial alternating current power supply AC, the dynamicrange of the voltage that is detected widens.

FIG. 6C illustrates a relationship between the effective value of thealternating-current voltage and the pulse width. In the secondembodiment, the voltage applied to the gate terminal of the FET Q3 isdesigned to depend substantially on resistors only. As can be seen fromthe fact that the difference in PW1, PW2, and PW3 becomes smaller, inthe second embodiment, the variation in results of voltage detection bythe circuit component is significantly suppressed as compared to thefirst embodiment. Also, the difference in the voltage level of thecommercial alternating current power supply AC is represented by the sumof two pieces of information: the gradient (dv/dt) of the voltage andthe direct-current voltage generated by the voltage generation unit 503.Accordingly, the amount of change in the pulse width in relation to thechange in voltage of the commercial alternating current power supply ACin the second embodiment becomes larger as compared to in the firstembodiment.

In this way, the voltage generation unit 503 fulfills a role of causingthe voltage detection precision to improve by making larger the amountof change in the pulse width in relation to the change in voltage of thecommercial alternating current power supply AC. However, the voltagegeneration unit 503 is not essential and may be omitted. It may bedetermined whether the voltage generation unit 503 is necessary or notin accordance with what degree of dynamic range in voltage detection isnecessary.

Third Embodiment

In a third embodiment, an edge indicating a zero cross and an edgeindicating a voltage level of the alternating-current voltage are eachgenerated by a FET. In other words, by making the rising edge a steeperedge, the detection precision of the zero cross is improved.

FIG. 7 illustrates the detection apparatus 100 of the third embodiment.The alternating-current voltage of the commercial alternating currentpower supply AC is applied to a rectification smoothing circuit 701. Ahalf wave rectification is performed on the alternating current by aresistor R12 and a diode D5 in the rectification smoothing circuit 701resulting in a pulsating flow, and the pulsating flow is converted intoa direct current by smoothing by a capacitor C5. The direct-currentvoltage that is produced between the two ends of the capacitor C5functions as a voltage source of the photocoupler PC. The direct-currentvoltage is applied to the anode of the light emitting diode D1 of thephotocoupler PC via a current-limiting resistor R1 and a FET Q4.Accordingly, the light emitting diode D1 of the third embodiment is keptin a state in which it can conduct electricity at all times, and thelight emitting diode D1 does not function as a direct switch element forcreating an edge. In other words, whether the FET Q4, which is connectedin series with the diode D1, conducts or does not conduct electricitycontrols whether the light emitting diode D1 conducts or does notconduct electricity. The transient response for whether the FET Q4conducts or does not conduct electricity is typically fast compared tothe transient response of the light emitting diode D1. Accordingly, inthe third embodiment, the rising edge of the pulse signal becomes steepcompared to in the first embodiment. By making the rising edge a steepedge, the effect of variation in the voltage detection threshold in theinput port 104 on edge detection becomes smaller. The result of this isthat zero cross detection precision becomes higher.

A resistor R13 and a resistor R14 form a voltage-dividing circuit thatdivides an alternating-current voltage supplied from the commercialalternating current power supply AC. The voltage generated by theresistor R13 and the resistor R14 is applied to the gate of the FET Q4.The FET Q4 operates so as to form a rising edge which indicates the zerocross timing of the alternating-current voltage of the commercialalternating current power supply AC. Accordingly, the FET Q4 whose gatevoltage is on the order of several V is selected.

A Zener diode D6 conducts electricity when a forward current flowstherethrough when the alternating-current voltage from the commercialalternating current power supply AC is a negative voltage. Thereby, anegative voltage of the capacitor C5 is suppressed to the forwardvoltage of the Zener diode D6. When the alternating-current voltage ofthe commercial alternating current power supply AC is a positivevoltage, the Zener diode D6 suppresses the positive voltage of thecapacitor C5 to a breakdown voltage. This is particularly useful when ahigh voltage that is outside specifications is outputted from thecommercial alternating current power supply AC. A voltage detection unit106 c is configured by a high-pass filter (HPF) 703 and an FET Q5. TheHPF 703 is configured by a capacitor C6 and a resistor R15. The HPF 703generates a voltage correlated with the alternating-current voltage andhaving a phase that is more advanced than the phase of thealternating-current voltage. The FET Q5 can turn off the light emittingdiode D1 forcibly because the FET Q5 is connected with the lightemitting diode D1 in parallel. The voltage detection unit 106 c forms arising edge by the FET Q5 conducting electricity in accordance with thevoltage level of the alternating-current voltage.

FIG. 8A illustrates a state of each voltage waveform W1 to W3 and theFET Q5 in the third embodiment. Note that W2 is a voltage waveform of avoltage applied to the FET Q5. W6 indicates whether the FET Q5 conductselectricity (ON) or does not conduct electricity (OFF). The FET Q4enters a conductive state when the voltage of the commercial alternatingcurrent power supply AC exceeds a predetermined voltage. Accordingly,when, at the zero cross timing, the FET Q4 switches from conductingelectricity to not conducting electricity, the light emitting diode D1turns off, and a rising edge is formed.

The FET Q4 is connected in parallel with the FET Q5. Accordingly, onlywhen the FET Q5 is in a non-conductive state is a forward voltageapplied to the light emitting diode D1 and the FET Q4 able to form arising edge. As FIG. 8A illustrates, when a zero cross occurs in thevoltage waveform W1 when the FET Q5 is in a non-conductive state (OFF),the FET Q4 switches from a conductive state to a non-conductive state,and the rising edge is formed. As FIG. 8A illustrates, when the FET Q5is in a conductive state (ON), the rising edge is not formed even if azero cross occurs.

As described above, the phase advances by the alternating-currentvoltage of the commercial alternating current power supply AC passingthrough the HPF 703. The cut-off frequency of the HPF 703 is set so thatthe phase of the alternating-current voltage advances by between severaltens of degrees and 90 degrees approximately in the range from 50 Hz to60 Hz which is the frequency of the alternating-current voltage. Thewaveform of the alternating-current voltage of the commercialalternating current power supply AC becomes the voltage waveform W2 bypassing through the HPF 703. When the gate voltage whose phase isadvanced due to passing through the HPF 703 exceeds the gate threshold(example: 3V), between the drain and the source of the FET Q5transitions from a non-conductive state and a conductive state. By theHPF 703 advancing the phase of the voltage, the conductive timing andnon-conductive timing of the FET Q5 advance in relation to those of theFET Q4 respectively. In the third embodiment, the diode D1 turns off anda rising edge indicating a zero cross is formed by the FET Q4transitioning from a conductive state to a non-conductive state.Accordingly, the state of the FET Q5 must be a non-conductive state whenthe FET Q4 transitions from a conductive state to a non-conductivestate. Accordingly, by the HPF 703, the timing at which the FET Q5transitions into a non-conductive state is made to be earlier than whenthe FET Q4 transitions into a non-conductive state. Also, a falling edgefor notifying the voltage level is formed when the light emitting diodeD1 turns on due to the FET Q5 transitioning from a conductive state intoa non-conductive state. Accordingly, the state of the FET Q5 must be aconductive state when the FET Q4 transitions from a conductive state toa non-conductive state. Since, by the HPF 703, the timing at which theFET Q5 transitions into a non-conductive state is made to be earlierthan when the FET Q4 transitions into a non-conductive state, thiscondition is also satisfied.

FIG. 8B illustrates voltage waveforms W1 through W3 where the voltage ofthe commercial alternating current power supply AC is caused to changein four 20V increments in the range from 80V to 140V. The timing of therising edge generated by the FET Q4 ceasing to conduct electricity doesnot change much even though the voltage level of the commercialalternating current power supply AC changes. Meanwhile, the timing atwhich the gate voltage of the FET Q5 exceeds the gate threshold changesgreatly depending on the voltage of the commercial alternating currentpower supply AC. That is, the timing of the falling edge generated bythe FET Q5 ceasing to conduct electricity changes greatly according tothe voltage of the commercial alternating current power supply AC. Notethat, the timing at which the FET Q5 begins to conduct electricitychanges greatly depending on the voltage of the commercial alternatingcurrent power supply AC. Because the HPF 703 is designed so that the FETQ4 invariably does not conduct electricity when the FET Q5 begins toconduct electricity, the pulse signal does not depend on the timing atwhich the FET Q5 begins to conduct electricity.

In the third embodiment, the capacitor C5 is being used in the voltagedetection unit 106 c similarly to in the first embodiment. Accordingly,the voltage detection result is easily influenced by variation in thecapacitor C5. Accordingly, a variable resistor may be employed as theresistor R15. Voltage detection precision increases by setting theresistance value of the variable resistor so as to reduce variation inthe capacitance of the capacitor C5.

Fourth Embodiment

The fourth embodiment increases voltage detection precision by combiningthe zero cross detection unit of the third embodiment and the voltagedetection unit of the second embodiment. In the third embodiment, theHPF 703 of the voltage detection unit 106 c is interposed in relation tothe gate of the FET Q5, and therefore the falling edge is influenced bythe HPF 703. Accordingly, in the fourth embodiment, in place of thevoltage detection unit 106 c, a voltage detection unit similar to thevoltage detection unit 106 b of the second embodiment is employed.

FIG. 9 illustrates the detection apparatus 100 of the fourth embodiment.A zero cross detection unit 101 c is the same as the zero crossdetection unit used in the third embodiment. A voltage detection unit106 d is formed by modifying part of the voltage detection unit 106 b ofthe second embodiment. As FIG. 9 illustrates, the zero cross detectionunit 101 c has the rectification smoothing circuit 701 that functions asa voltage generation unit for generating a direct-current voltage.Accordingly, the voltage generation unit 503 illustrated in FIG. 5 isunnecessary. The direct-current voltage generated by the rectificationsmoothing circuit 701 is applied to the gate terminal of a FET Q6 via aresistor R16. Because this direct-current voltage is a voltage thatexceeds the gate threshold of the FET Q6, the FET Q6 is kept in a statein which it can conduct electricity at all times. The drain terminal ofthe FET Q3 is connected to the gate terminal of the FET Q6 via acurrent-limiting resistor R17. The FET Q3 and the FET Q6 substantiallyform an inversion circuit. If the state of the FET Q3 is a conductivestate, the gate voltage of the FET Q6 becomes less than or equal to thegate threshold, and the state of the FET Q6 is a non-conductive state.Meanwhile, if the state of the FET Q3 is a non-conductive state, thegate voltage of the FET Q6 exceeds the gate threshold, and the state ofthe FET Q6 is a conductive state. In this way, because the FET Q6 isconnected in parallel with the light emitting diode D1 and the FET Q4,it contributes to forming the falling edge similarly to the FET Q5 inthe fourth embodiment.

FIG. 10A illustrates voltage waveforms in the fourth embodiment. W2 is avoltage waveform of a gate voltage of the FET Q3. W10 is a voltagewaveform of a gate voltage of the FET Q6. As FIG. 9 illustrates, the FETQ4 and the FET Q6 are connected in parallel to the commercialalternating current power supply AC. When the FET Q4 is in a conductivestate, the light emitting diode D1 turns on and the falling edge isgenerated by the FET Q6 transitioning from a conductive state to anon-conductive state. Thereby, the voltage level of thealternating-current voltage is transferred to the microcomputer 105.Note that the FET Q6 is kept in a state in which it can conductelectricity at all times. Accordingly, the state of the FET Q6 iscontrolled by the FET Q3. During a period when the FET Q3 is in aconductive state, the FET Q6 is kept in a non-conductive state. In otherwords, as the voltage waveforms W2 and W3 illustrate, when the gatevoltage of the FET Q3 exceeds the gate threshold, the FET Q6 transitionsinto a non-conductive state. Also, when the gate voltage of the FET Q3becomes less than or equal to the gate threshold, the FET Q6 transitionsinto a conductive state.

When the FET Q6 is in a non-conductive state, the gate voltage of theFET Q4 less than or equal to the gate threshold, and thereby the FET Q4transitions from a conductive state into a non-conductive state, thelight emitting diode D1 turns off, and the rising edge is formed.Thereby, the zero cross timing of the alternating-current voltage istransferred to the microcomputer 105.

FIG. 10B illustrates voltage waveforms W1, W2, and W10 which are forwhen the voltage of the commercial alternating current power supply ACis caused to change in four 20V increments in the range from 80V to140V. The position of the rising edge generated by the FET Q4 ceasing toconduct electricity does not change much even though the voltage levelof the commercial alternating current power supply AC changes.Meanwhile, the timing at which the gate voltage of the FET Q6 becomesless than or equal to the gate threshold changes greatly depending onthe voltage of the commercial alternating current power supply AC. Theposition of the falling edge generated by the FET Q6 transitioning froma conductive state to a non-conductive state changes greatly dependingon the voltage of the commercial alternating current power supply AC. Inthe fourth embodiment, the timing at which the gate voltage of the FETQ6 becomes less than or equal to the gate threshold substantially onlydepends on resistors. The resistors are circuit elements for whichresistance value variation is typically small, but capacitors and coilsare circuit elements for which capacitance value and inductance valuevariation is large. Such circuit element variation lowers voltagedetection precision. Only resistors are interposed in the fourthembodiment, and no capacitors or coils are interposed. Accordingly, inthe fourth embodiment, it is possible to detect the commercialalternating current power supply AC voltage at higher precision comparedto the third embodiment.

Fifth Embodiment

In the fifth embodiment, the driving source of the photocoupler PC inthe fourth embodiment is changed from a direct-current voltage to analternating-current voltage. FIG. 11 illustrates the detection apparatus100 of the fifth embodiment. The zero cross detection unit 101 a is thesame as the zero cross detection unit used in the first embodiment andthe second embodiment. A voltage detection 106 e is formed by combiningthe voltage generation unit 503 of the second embodiment with thevoltage detection unit 106 d of the fourth embodiment. Specifically, thedirect-current voltage generated by the voltage generation unit 503 isprovided via the resistor R16 to the gate terminal of the FET Q6. Thedirect-current voltage generated by the voltage generation unit 503 isset to a voltage that is higher than the gate threshold of the FET Q6.Accordingly, the FET Q6 is kept in a state in which it can conductelectricity at all times. The drain of the FET Q3 is connected to thegate terminal of the FET Q6 via the current-limiting resistor R17.Accordingly, if the FET Q3 transitions into a conductive state, the gatevoltage of the FET Q6 becomes less than or equal to the gate threshold,and the state of the FET Q6 transitions into a non-conductive state.

FIG. 12A illustrates voltage waveforms W1, W2, and W10 according to thefifth embodiment. It can be seen, comparing to FIG. 10A, that thevoltage waveforms W1, W2, and W10 are the same in FIG. 12A. In otherwords, the circuit configuration of the zero cross detection unit 101 adoes not influence the operation of the voltage detection 106 e.

In the fifth embodiment, control of whether the light emitting diode D1of the photocoupler PC conducts electricity or does not conductelectricity is controlled by the light emitting diode D1 itself.Accordingly, the gradient of the rising edge of the pulse signal in thefifth embodiment is smoother than the gradient of the rising edge of thefourth embodiment.

FIG. 12B illustrates voltage waveforms W1, W2, and W10 where the voltageof the commercial alternating current power supply AC is caused tochange in four 20V increments in the range from 80V to 140V. In thefirst embodiment and the second embodiment, the FETs Q2 and Q3 whichgenerate the falling edge of the pulse signal are connected to thecommercial alternating current power supply AC. Meanwhile, the gate ofthe FET Q3 that controls the timing of the falling edge in the fifthembodiment is connected to the output of the voltage generation unit 503(several V to several tens of V). Accordingly, it is possible to employa FET whose tolerable voltage is lower than that of the FETs in thefirst embodiment and the second embodiment as the FET Q3. Note that inplace of the FET Q3, a shunt regulator with low tolerable voltage andlow threshold voltage variation may also be employed. Thereby, thevoltage detection precision of the commercial alternating current powersupply AC is further improved.

Sixth Embodiment

The sixth embodiment employs a configuration that combines the zerocross detection unit 101 c used in the third and fourth embodiments anda voltage detection unit which has hysteresis characteristics. FIG. 13illustrates the detection apparatus 100 of the sixth embodiment. Avoltage detection unit 106 f has a comparator CP which has hysteresischaracteristics. A resistor R18 and a resistor R19 are avoltage-dividing circuit that divides the direct-current voltagegenerated by the rectification smoothing circuit 701 and applies theoutput voltage to a non-inverting input terminal (+ terminal) of thecomparator CP. This becomes a reference voltage of the comparator CP.The aforementioned resistor R13 and resistor R14 are a voltage-dividingcircuit that divides the alternating-current voltage of the commercialalternating current power supply AC and applies the output voltage to aninverting input terminal (− terminal) of the comparator CP. Thereference voltage inputted into the non-inverting input terminal (+terminal) is a voltage that corresponds to the alternating-currentvoltage 85V (≈60V×√2) of the commercial alternating current power supplyAC, for example. This is for causing the load 320, which may be an AC/DCconverter, to stop when the alternating-current voltage becomes lessthan 85V. Accordingly, the reference voltage may be set in accordancewith the load.

FIG. 14A illustrates voltage waveforms in the sixth embodiment. W13indicates a voltage waveform of a gate voltage of a FET Q7. W14indicates an output state of the comparator CP. Output of the comparatorCP becomes a high impedance (Hiz) in a case where the voltage of thecommercial alternating current power supply AC is less than 85V. In acase where the output of the comparator CP is Hiz, a direct-currentvoltage is applied by a pull-up resistor R20 to the gate terminal of theFET Q7. Thereby, the FET Q7 enters a conductive state. When the FET Q7enters a conductive state, the light emitting diode D1 turns on, and thepulse signal becomes a low level. In the sixth embodiment, a fallingedge indicates a zero cross timing.

In a case where the voltage of the commercial alternating current powersupply AC is +85V or more, the output of the comparator CP isapproximately 0V (L), and therefore the FET Q7 is in a non-conductivestate. When the FET Q7 enters a non-conductive state, the light emittingdiode D1 turns on, and the pulse signal becomes a high level. In thesixth embodiment, the rising edge indicates the voltage level.

When the output of the comparator CP becomes L, it is equivalent to astate in which the resistor R21 is connected to the resistor R19 inparallel. The resistance value of the resistor R21 is set to besufficiently low as compared to the resistance value of the resistorR19. Accordingly, the reference voltage inputted into the non-invertinginput terminal (+ terminal) in a case where the output of the comparatorCP became L becomes a voltage that corresponds to approximately 0V inthe voltage of the commercial alternating current power supply AC. Theoutput of the comparator CP that once outputted L does not reverse toHiz again when the voltage of the commercial alternating current powersupply AC does not decrease to approximately 0V. In other words, theoperation of the comparator CP is that the output is L in a case wherethe voltage of the commercial alternating current power supply AC is 85Vor more and there are hysteresis characteristics such as outputting Hizin a case where the voltage of the commercial alternating current powersupply AC is approximately 0V or less.

FIG. 14B illustrates voltage waveforms W1, W3, and W13 where the voltageof the commercial alternating current power supply AC is caused tochange in four 20V increments in the range from 80V to 140V. By thehysteresis characteristics of the comparator CP, the rising edge changesin accordance with the voltage of the commercial alternating currentpower supply AC, and the falling edge does not depend on the voltage ofthe commercial alternating current power supply AC. In this way, in thesixth embodiment, the information that the rising edge conveys and theinformation that the falling edge conveys differ from in the firstembodiment through to the fifth embodiment.

In the first embodiment through to the fifth embodiment, an element thatgenerates the falling edge and an element that generates the rising edgeare provided separately. In the sixth embodiment, the falling edge andthe rising edge can be generated by the FET Q7 on its own. Accordingly,the sixth embodiment can reduce the number of switch elements ascompared to the third embodiment through to the fifth embodiment.

Seventh Embodiment

FIG. 15 illustrates an intermediate transfer method image formingapparatus 1 to which the detection apparatus 100 and the microcomputer105 can be applied. The image forming apparatus 1 may be an imageforming apparatus for forming a monochrome image, but here it is anelectrophotographic type image forming apparatus that forms a multicolorimage by color mixing of a plurality of colorants. The image formingapparatus 1 uses toner of four colors such as yellow (Y), magenta (M),cyan (C), and black (BK). Characters indicating a color are added to theend of reference numerals in FIG. 15, but these characters are omittedwhen matters common to the four colors are explained.

Photosensitive drums 6C, 6M, 6Y, and 6BK are arranged at regularintervals to each other, and are image carriers for carrying anelectrostatic latent image or a toner image. An engine controller 1502has the microcomputer 105, and controls a power supply apparatus 1500that the image forming apparatus 1 comprises and the load 320 such as amotor, an actuator, a solenoid, a sensor, a heater 15, or the like. Thepower supply apparatus 1500 is connected via a power supply cable 1501to the commercial alternating current power supply AC. The power supplycable 1501 functions as an input unit of the alternating-currentvoltage. The power supply apparatus 1500 has the detection apparatus100, an AC/DC converter, a DC/DC converter, or the like.

A primary charger 2 charges the surface of a photosensitive drum 6uniformly by using a charge voltage supplied from the power supplyapparatus 1500. An optical scanning apparatus 3 emits toward thephotosensitive drums 6 a light beam (a laser beam) L that isrespectively modulated based on an input image. The light beam (laserbeam) L forms an electrostatic latent image on the surface of thephotosensitive drum 6. The engine controller 1502 controls the powersupply apparatus 1500 to generate a developing voltage, and supplies thedeveloping voltage to a developer 4. The developers 4 respectively causecyan, magenta, yellow, and black toner to adhere to the electrostaticlatent image, through a sleeve or a blade to which the developingvoltage is applied. By this, the electrostatic latent image is developedand a developer image (a toner image) is formed.

A sheet feed roller 8 is driven by a motor or a solenoid that iscontrolled by the microcomputer 105. The sheet feed roller 8 feedssheets P that are accommodated in a feeding tray 7 one at a time. Aregistration roller 9 is driven by a motor that is controlled by themicrocomputer 105. The registration roller 9 feeds sheets P to asecondary transfer unit in synchronism with an image write start timing.

The engine controller 1502 controls the power supply apparatus 1500 togenerate a primary transfer voltage, and supplies the primary transfervoltage to a primary transfer roller 5. The primary transfer roller 5primary transfers the toner image carried by the photosensitive drum 6onto an intermediate transfer belt 10. The primary transfer voltageapplied to the primary transfer roller 5 promotes the primary transferof the toner image. The intermediate transfer belt 10 functions as anintermediate transfer body. A driving roller 11 is a roller that causesthe intermediate transfer belt 10 to rotate. A secondary transfer unithas a secondary transfer roller 14. The engine controller 1502 controlsthe power supply apparatus 1500 to generate a secondary transfervoltage, and supplies the secondary transfer roller 14. In the secondarytransfer unit, by the intermediate transfer belt 10 and the secondarytransfer roller 14 conveying while pinching the sheet P, the multicolortoner image carried on the intermediate transfer belt 10 is secondarytransferred to the sheet P. The secondary transfer voltage promotes thesecondary transfer. After this, the sheets P are conveyed to a fixingdevice 12. The fixing device 12 applies heat and pressure to the tonerimage carried on the sheet P to cause fixing. A discharging roller 13discharges the sheet P on which the image is formed. The fixing device12 has the heater 15, and temperature is controlled by the microcomputer105. The microcomputer 105 controls the power supplied by the heater 15by controlling the aforementioned wave number.

SUMMARY

As explained using the first to sixth embodiments, the detectionapparatus 100 generates a superimposition signal in which informationindicating a timing of a zero cross in an alternating-current voltageand information indicating a voltage level of the alternating-currentvoltage are superimposed. Thereby it becomes possible to reduce thenumber of signal lines for transferring the zero cross timing and thevoltage level. For example, the detection apparatus 100 may have a pulsegeneration circuit that generates, as a superimposition signal, a pulsesignal including a first edge that indicates a timing of a zero cross inan alternating-current voltage and a second edge for which a timeinterval in relation to the first edge changes in accordance with thevoltage level of the alternating-current voltage.

This kind of pulse generation circuit has a first edge circuit thatgenerates the first edge at a timing of a zero cross and a second edgecircuit that generates the second edge at a timing according to agradient of the alternating-current voltage. The zero cross detectionunits 101 a and 101 c are examples of the first edge circuit. Also, thevoltage detection unit 106 a and 106 f are examples of the second edgecircuit. The first edge circuit generates a first edge when the voltagelevel of the alternating-current voltage is a first level. As describedusing FIG. 2A and the like, the first level is the forward voltage VF ofthe light emitting diode D1 or the like. The first level in FIG. 7 isthe gate threshold of the FET Q4. As described above, the forwardvoltage VF is sufficiently small compared to the effective value of thealternating-current voltage, and can be estimated to be about 0V.Accordingly, a zero cross point is detected accurately.

As described using FIG. 2B and the like, the second edge circuit detectsa second level which is a voltage level of the alternating-currentvoltage or a voltage correlated to the alternating-current voltage, andgenerates a second edge in accordance with the second level. The secondlevel is a gate threshold of the FET Q2 or the like. The gradient of thealternating-current voltage changes in accordance with the voltage levelof the alternating-current voltage. In other words, it changes inaccordance with the timing at which the voltage correlated to thealternating-current voltage exceeds the gate threshold and the voltagelevel of the alternating-current voltage. By using such a switch elementproperty, the voltage level is reflected in the second edge.

As illustrated in FIG. 1, the first edge circuit has a first switchelement that conducts electricity when the alternating-current voltageexceeds the threshold, and does not conduct electricity if thealternating-current voltage does not exceed the threshold. The lightemitting diode D1 is one example of the first switch element. The secondedge circuit has a delay circuit and a second switch element. The delaycircuit is a circuit for delaying the phase of the alternating-currentvoltage. The second switch element is a switch element that has acontrol terminal to which an alternating-current voltage whose phase isdelayed is applied and that switches between a conductive state and anon-conductive state in accordance with the voltage applied to thecontrol terminal. A gate terminal is an example of the control terminal.The level detection unit 107 that configures the low-pass filter is oneexample of the delay circuit. The FET Q2 is one example of the secondswitch element. As FIG. 1 illustrates, the first switch element and thesecond switch element are connected in series. As FIG. 2B illustrates,the first edge circuit generates a first edge that indicates the timingof a zero cross by the first switch element not conducting electricity.As FIG. 2A illustrates, the second edge circuit generates a second edgethat indicates the voltage level by the second switch element changingfrom a non-conductive state to a state in which it can conductelectricity in accordance with the voltage level of thealternating-current voltage when the first switch element is in aconductive state. Here, the first edge is a rising edge generated by thepulse signal switching from low level to high level. Here, the secondedge is a falling edge generated by a switch from high level to lowlevel. The relationship between these edges may be inverted.

As described in the second embodiment, the first edge circuit has afirst switch element that conducts electricity when thealternating-current voltage exceeds the threshold, and does not conductelectricity if the alternating-current voltage does not exceed thethreshold. The second edge circuit may have a first voltage dividingunit, a delay circuit, an addition circuit, a second switch element, orthe like. As FIG. 5 illustrates, the voltage detection unit 106 b is anexample of the second edge circuit. The level detection unit 501 is oneexample of a first voltage dividing unit that generates a voltage thatcorrelates to the alternating-current voltage by dividing thealternating-current voltage. The timing adjusting unit 502 is oneexample of a delay circuit that delays the phase of thealternating-current voltage. The resistor R7 is one example of anaddition circuit that adds the voltage outputted from the first voltagedividing unit and the voltage outputted from the delay circuit. The FETQ3 is one example of the second switch element which has a controlterminal to which the voltage outputted from the addition circuit isapplied and that switches between a conductive state and anon-conductive state in accordance with the voltage applied to thecontrol terminal. In the second embodiment as well, the first switchelement and the second switch element are connected in series. Asillustrated in FIG. 6B, the first edge circuit generates a first edgethat indicates the timing of a zero cross by the first switch elementnot conducting electricity. The second edge circuit generates a secondedge that indicates a voltage level by the second switch elementchanging from a non-conductive state to a conductive state in accordancewith the voltage level of the voltage outputted from the additioncircuit when the first switch element is conducting electricity.

As described in the second embodiment, the second edge circuit may havea rectification smoothing circuit that generates a direct-currentvoltage by rectification and smoothing of the alternating-currentvoltage, and applies the direct-current voltage to the control terminalof the second switch element. The voltage generation unit 503 is oneexample of the rectification smoothing circuit. By employing such arectification smoothing circuit, the detection precision of the voltagelevel is further improved. As described in the second embodiment, thevoltage generation unit 503 may have a second voltage dividing unit thatdivides the direct-current voltage and applies it to the controlterminal of the second switch element. As FIG. 5 illustrates, theresistor R8 and the resistor R9 are one example of the second voltagedividing unit.

As the third embodiment illustrates, the first edge circuit may berealized by the zero cross detection unit 101 c. The rectificationsmoothing circuit 701 is one example of a rectification smoothingcircuit that generates a direct-current voltage by rectification andsmoothing the alternating-current voltage. The FET Q4 is one example ofa first switch element that has a control terminal that operates bybeing supplied direct-current voltage and to which a voltage correlatedwith the alternating-current voltage is applied, and that conductselectricity when the voltage correlated to the alternating-currentvoltage exceeds a threshold, and does not conduct electricity if thevoltage correlated to the alternating-current voltage does not exceedthe threshold. The second edge circuit may be realized by the voltagedetection unit 106 c. The HPF 703 is one example of a phase circuit thatadvances the phase of the alternating-current voltage. The FET Q5 is oneexample of a second switch element which has a control terminal to whichthe alternating-current voltage whose phase was advanced by the phasecircuit is applied and that switches between a conductive state and anon-conductive state in accordance with the voltage applied to thecontrol terminal. As FIG. 7 illustrates, the first switch element andthe second switch element are connected in parallel. The zero crossdetection unit 101 c generates the first edge which indicates the timingof the zero cross by the first switch element transitioning from aconductive state to a non-conductive state. As FIG. 8A illustrates, thevoltage detection unit 106 c generates a second edge which indicates thevoltage level by the second switch element transitioning to anon-conductive state from a conductive state in accordance with thevoltage level of the alternating-current voltage at a time when thefirst switch element is in a state in which it can conduct electricity.As FIG. 7 illustrates, the first switch element may be formed by aseries connection between the light emitting diode D1 which is arectification element and the FET Q4 which is a semiconductor switch.

As described in the fourth embodiment, the first edge circuit may berealized by the zero cross detection unit 101 c. The second edge circuitmay be realized by the voltage detection unit 106 d. As FIG. 9illustrates, the level detection unit 501 is one example of a firstvoltage dividing unit that generates a voltage that correlates to thealternating-current voltage by dividing the alternating-current voltage.The timing adjusting unit 502 is one example of a delay circuit thatdelays the phase of the alternating-current voltage. The resistor R7 isone example of an addition circuit that adds the voltage outputted fromthe first voltage dividing unit and the voltage outputted from the delaycircuit. The FET Q3 is one example of the second switch element whichhas a control terminal to which the voltage outputted from the additioncircuit is applied and that switches between a conductive state and anon-conductive state in accordance with the voltage applied to thecontrol terminal. The FET Q6 is one example of a third switch elementthat has a control terminal to which is applied a direct-current voltagewhich is generated from the alternating-current voltage and for whichthe second switch element controls application and non-application ofthe direct-current voltage, and that is connected in parallel with thefirst switch element. The voltage detection unit 106 d generates asecond edge that indicates a voltage level by the third switch elementtransitioning from a conductive state to a non-conductive state by thesecond switch element transitioning from a non-conductive state to aconductive state in accordance with the voltage level of thealternating-current voltage when the first switch element is in a statein which it can conduct electricity. This is exemplified in FIG. 10A andFIG. 10B.

As described in the fifth embodiment, the first edge circuit may be thezero cross detection unit 101 a. The second edge circuit may be thevoltage detection 106 e. As FIG. 9 illustrates, the level detection unit501 is one example of a first voltage dividing unit that generates avoltage that correlates to the alternating-current voltage by dividingthe alternating-current voltage. The timing adjusting unit 502 is adelay circuit that delays the phase of the alternating-current voltage.The resistor R7 is one example of an addition circuit that adds thevoltage outputted from the first voltage dividing unit and the voltageoutputted from the delay circuit. The FET Q3 is one example of thesecond switch element which has a control terminal to which the voltageoutputted from the addition circuit is applied and that switches betweena conductive state and a non-conductive state in accordance with thevoltage applied to the control terminal. The FET Q6 is one example of athird switch element that has a control terminal to which is applied adirect-current voltage which is generated from the alternating-currentvoltage and for which the second switch element controls application andnon-application of the direct-current voltage, and that is connected inparallel with the first switch element. The voltage detection 106 egenerates a second edge that indicates a voltage level by the thirdswitch element transitioning from a conductive state to a non-conductivestate in accordance with the second switch element transitioning from anon-conductive state to a conductive state for the voltage level of thealternating-current voltage when the first switch element is in a statein which it is conducting electricity.

As described in the sixth embodiment, the pulse generation circuit mayhave the FET Q7 which is a switch element and a comparator CP. Thecomparator CP has hysteresis characteristics, and switches between aconductive state and a non-conductive state of the switch element inaccordance with a voltage that is correlated with thealternating-current voltage. As FIG. 14A illustrates, the comparator CPcauses the switch element to transition from a non-conductive state to aconductive state so that the switch element generates a first edge at azero cross timing. As FIG. 14B illustrates, the comparator CP causes theswitch element to transition from a conductive state to a non-conductivestate so that the second edge is generated at a timing according to thegradient of a voltage correlated with the alternating-current voltage.Note that in the sixth embodiment, the rising edge corresponds to thesecond edge and the falling edge corresponds to the first edge.

As FIG. 3 and FIG. 15 illustrate, the microcomputer 105 and the enginecontroller 1502 are examples of controllers. The input port 104 is oneexample of an input unit into which is inputted a pulse signal includinga first edge that indicates a timing of a zero cross in analternating-current voltage and a second edge for which a time intervalin relation to the first edge changes in accordance with the voltagelevel of the alternating-current voltage. The second counter 304 is oneexample of a measurement unit that measures a time interval between afirst edge and a second edge. Here, the time interval is measured fromthe second edge until the first edge. The voltage determination unit 305is one example of a determination unit that determines a voltage levelof an alternating-current voltage based on a time interval measured bythe measurement unit. The load control unit 301 is one example of acontrol unit that controls a load using the zero cross timing that thefirst edge indicates and the voltage level. In this way, themicrocomputer 105 is enabled to obtain the zero cross timing and thevoltage level by a single input port 104.

As described using FIG. 15, the photosensitive drum 6 is one example ofan image carrier. The primary charger 2 is one example of a chargingunit for uniformly charging the image carrier. The optical scanningapparatus 3 is one example of an exposure unit for forming anelectrostatic latent image by exposing an image carrier. The developer 4is one example of a developer unit that forms a toner image bydeveloping an electrostatic latent image. The primary transfer roller 5,the intermediate transfer belt 10 and the secondary transfer roller 14are one example of a transfer unit for transferring a toner image to asheet. Note that the toner image may be transferred directly to a sheetP from the photosensitive drum 6. In such a case the intermediatetransfer belt 10 and the secondary transfer roller 14 are not necessary.The fixing device 12 is one example of a fixing unit that comprises aheating unit and that causes a toner image to be fixed to a sheet byheating it using the heating unit. The heater 15 is one example of theheating unit. The detection apparatus 100 is one example of a generationunit that generates a pulse signal including a first edge that indicatesa timing of a zero cross in an alternating-current voltage supplied froman alternating power supply and a second edge for which a time intervalin relation to the first edge changes in accordance with the voltagelevel of the alternating-current voltage. The microcomputer 105 is oneexample of a control unit that receives a pulse signal, obtains a zerocross timing of the alternating-current voltage and the voltage level ofthe alternating-current voltage from the pulse signal, and controls thepower supplied to the heating unit based on the zero cross timing andthe voltage level.

One example of a method of controlling the heating unit is a method thatcontrols the wave number for power on/off control for each half periodof the alternating-current voltage in accordance with the zero crosstiming. Another example is a phase control type that supplies heat bycontrolling the on time in a half period of the alternating-currentvoltage. Note that it is possible to employ a hybrid control method thatcombines the wave number control method and the phase control type.

Also, a cooling fan may be employed as the load.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Applications No.2017-030245, filed Feb. 21, 2017 and No. 2017-237094, filed Dec. 11,2017, which are hereby incorporated by reference herein in theirentirety.

What is claimed is:
 1. A detection apparatus comprising: analternating-current voltage input unit; a generation circuit configuredto generate a pulse signal of which level is switched between a firstlevel and a second level, wherein the pulse signal includes informationindicating a timing of a zero cross in an alternating-current voltageinputted into the input unit and information indicating a voltage valueof the alternating-current voltage, wherein the generation circuitincludes a first circuit configured to switch the level of the pulsesignal from the first level to the second level and a second circuitconfigured to switch the level of the pulse signal from the second levelto the first level; and a determination unit configured to determine thetiming of the zero cross based on a first timing at which the firstcircuit switches the level of the pulse signal and to determine thevoltage value of the alternating-current voltage based on a time periodbetween the first timing and a second timing at which the second circuitswitches the level of the pulse signal.
 2. The detection apparatusaccording to claim 1, wherein the generation circuit including the firstand the second circuits has a pulse generation circuit that generates,as the pulse signal, the pulse signal including a first edgecorresponding to the rising second timing and a second edgecorresponding to the fatting first timing, the first edge indicating thetiming of the zero cross in the alternating-current voltage, and thesecond edge indicating the voltage value of the alternating-currentvoltage by a time interval between the first edge and the second edgechanging in accordance with the voltage value of the alternating-currentvoltage.
 3. The detection apparatus according to claim 2, wherein thefirst circuit has a first edge circuit that generates the first edge atthe zero cross timing, and the second circuit has a second edge circuitthat generates the second edge at a timing according to a gradient ofthe alternating-current voltage.
 4. The detection apparatus according toclaim 3, wherein the first edge circuit generates the first edge whenthe voltage value of the alternating-current voltage is a first value.5. The detection apparatus according to claim 3, wherein the second edgecircuit detects a second value which is a voltage value of thealternating-current voltage or a voltage correlated to thealternating-current voltage, and generates the second edge in accordancewith the second value.
 6. The detection apparatus according to claim 3,wherein the first edge circuit has a first switch element that conductselectricity when the alternating-current voltage exceeds a threshold anddoes not conduct electricity if the alternating-current voltage does notexceed the threshold, the second edge circuit has a delay circuit thatdelays a phase of the alternating-current voltage and a second switchelement that has a control terminal to which the alternating-currentvoltage whose phase was delayed is applied and that switches between aconductive state and a non-conductive state in accordance with thevoltage applied to the control terminal, wherein the first switchelement is connected in series with the second switch element, whereinthe first edge circuit generates the first edge that indicates thetiming of the zero cross by the first switch element not conductingelectricity, and wherein the second edge circuit generates the secondedge that indicates the voltage value by the second switch elementchanging from a non-conductive state to a conductive state in accordancewith the voltage value of the alternating-current voltage when the firstswitch element is conducting electricity.
 7. The detection apparatusaccording to claim 3, wherein the first edge circuit has a first switchelement that conducts electricity when the alternating-current voltageexceeds a threshold and does not conduct electricity if thealternating-current voltage does not exceed the threshold, the secondedge circuit has a first voltage dividing unit that generates a voltagethat is correlated to the alternating-current voltage by dividing thealternating-current voltage; a delay circuit that delays a phase of thealternating-current voltage; an addition circuit that adds the voltageoutputted from the first voltage dividing unit and the voltage outputtedfrom the delay circuit; and a second switch element that has a controlterminal to which the voltage outputted from the addition circuit isapplied and that switches between a conductive state and anon-conductive state in accordance with the voltage applied to thecontrol terminal, and the first switch element is connected in serieswith the second switch element, the first edge circuit generates thefirst edge that indicates the timing of the zero cross by the firstswitch element not conducting electricity, and the second edge circuitgenerates the second edge that indicates the voltage level by the secondswitch element changing from a non-conductive state to a conductivestate in accordance with the voltage level of the voltage outputted fromthe addition circuit when the first switch element is conductingelectricity.
 8. The detection apparatus according to claim 7, whereinthe second edge circuit further has a rectification smoothing circuitthat generates a direct-current voltage by rectifying and smoothing thealternating-current voltage, and applies the direct-current voltage tothe control terminal of the second switch element.
 9. The detectionapparatus according to claim 8, wherein the rectification smoothingcircuit has a second voltage dividing unit that divides thedirect-current voltage and applies a result of the dividing to thecontrol terminal of the second switch element.
 10. The detectionapparatus according to claim 3, wherein the first edge circuit has arectification smoothing circuit that generates a direct-current voltageby rectifying and smoothing the alternating-current voltage, and a firstswitch element that has a control terminal that operates by beingsupplied the direct-current voltage and to which a voltage correlatedwith the alternating-current voltage is applied, and that conductselectricity when the voltage correlated to the alternating-currentvoltage exceeds a threshold, and does not conduct electricity if thevoltage correlated to the alternating-current voltage does not exceedthe threshold, and the second edge circuit has a phase circuit thatadvances a phase of the alternating-current voltage and a second switchelement that has a control terminal to which the alternating-currentvoltage whose phase was advanced by the phase circuit is applied andthat switches between a conductive state and a non-conductive state inaccordance with the voltage applied to the control terminal, the firstswitch element is connected in parallel with the second switch element,the first edge circuit generates the first edge that indicates thetiming of the zero cross by the first switch element transitioning froma conductive state to a non-conductive state, and the second edgecircuit generates the second edge that indicates the voltage level bythe second switch element transitioning from a conductive state to anon-conductive state in accordance with the voltage level of thealternating-current voltage when the first switch element is in a statein which the first switch element can conduct electricity.
 11. Thedetection apparatus according to claim 10, wherein the first switchelement is formed by a series connection between a rectification elementand a semiconductor switch.
 12. The detection apparatus according toclaim 3, wherein the first edge circuit has a rectification smoothingcircuit that generates a direct-current voltage by rectifying andsmoothing the alternating-current voltage, and a first switch elementthat has a control terminal that operates by being supplied thedirect-current voltage and to which a voltage correlated with thealternating-current voltage is applied, and that conducts electricitywhen the voltage correlated to the alternating-current voltage exceeds athreshold, and does not conduct electricity if the voltage correlated tothe alternating-current voltage does not exceed the threshold, and thesecond edge circuit has a first voltage dividing unit that generates avoltage that is correlated to the alternating-current voltage bydividing the alternating-current voltage; a delay circuit that delays aphase of the alternating-current voltage; an addition circuit that addsthe voltage outputted from the first voltage dividing unit and thevoltage outputted from the delay circuit; and a second switch elementthat has a control terminal to which the voltage outputted from theaddition circuit is applied and that switches between a conductive stateand a non-conductive state in accordance with the voltage applied to thecontrol terminal; and a third switch element that has a control terminalto which is applied a direct-current voltage which is generated from thealternating-current voltage and for which the second switch elementcontrols application and non-application of the direct-current voltage,and that is connected in parallel with the first switch element, and thefirst edge circuit generates the first edge that indicates the timing ofthe zero cross by the first switch element transitioning from aconductive state to a non-conductive state, and the second edge circuitgenerates the second edge that indicates the voltage level by the thirdswitch element transitioning from a conductive state to a non-conductivestate by the second switch element transitioning from a non-conductivestate to a conductive state in accordance with the voltage level of thealternating-current voltage when the first switch element is in a statein which the first switch element can conduct electricity.
 13. Thedetection apparatus according to claim 3, wherein the first edge circuithas a first switch element that conducts electricity when thealternating-current voltage exceeds a threshold and does not conductelectricity if the alternating-current voltage does not exceed thethreshold, and the second edge circuit has a first voltage dividing unitthat generates a voltage that is correlated to the alternating-currentvoltage by dividing the alternating-current voltage; a delay circuitthat delays a phase of the alternating-current voltage; an additioncircuit that adds the voltage outputted from the first voltage dividingunit and the voltage outputted from the delay circuit; a second switchelement that has a control terminal to which the voltage outputted fromthe addition circuit is applied and that switches between a conductivestate and a non-conductive state in accordance with the voltage appliedto the control terminal; and a third switch element that has a controlterminal to which is applied a direct-current voltage which is generatedfrom the alternating-current voltage and for which the second switchelement controls application and non-application of the direct-currentvoltage, and that is connected in parallel with the first switchelement, the first edge circuit generates the first edge that indicatesthe timing of the zero cross by the first switch element transitioningfrom a conductive state to a non-conductive state, and the second edgecircuit generates the second edge that indicates the voltage level bythe third switch element transitioning from a conductive state to anon-conductive state by the second switch element transitioning from anon-conductive state to a conductive state in accordance with thevoltage level of the alternating-current voltage when the first switchelement is conducting electricity.
 14. The detection apparatus accordingto claim 2, wherein the pulse generation circuit has a switch element,and a comparator that has hysteresis characteristics, and switchesbetween a conductive state and a non-conductive state of the switchelement in accordance with a voltage that is correlated to thealternating-current voltage, and the comparator causes the switchelement to transition from a non-conductive state to a conductive stateso that the switch element generates the first edge at the timing of thezero cross, and causes the switch element to transition from aconductive state to a non-conductive state so that the second edge isgenerated at a timing according to a gradient of the voltage that iscorrelated to the alternating-current voltage.
 15. The detectionapparatus according to claim 1, wherein the voltage value in a firstcase where the time period from the first timing of the pulse signal tothe next second timing of the pulse signal is a first value, and thevoltage value in a second case where the time period from the firsttiming of the pulse signal to the next second timing of the pulse signalis a second value smaller than the first value.